1. Field of Invention
The present invention relates to methacrolein, and more particularly to a catalyst composition and a producing process thereof for use in manufacturing methacrolein by using isobutene or t-butanol as the reacting agents to produce methacrolein with high activeness, high selectivity, and high stabilization properties.
2. Description of Related Arts
The oxidizing process of isobutene (or t-butanol) is widely used for manufacturing methacrolein in the industrialization production process of methyl methacrylate. Accordingly, there are two different processes for manufacturing methyl methacrylate by using C4 as the raw material. The first process includes a two-step oxidation process for isobutene (or t-butanol) to form methyl methacrylate, wherein the first step of oxidation of isobutene (or t-butanol) is to obtain methacrolein and the second step of oxidation of methacrolein is to obtain methylacrylic acid, such that the resulting methylacrylic acid reacts with methyl alcohol to form the methyl methacrylate through esterification. The second process includes a one-step oxidation process for isobutene (or t-butanol) to form methacrolein, which is then reacted with methanol (also commonly known as methyl alcohol) to form methyl methacrylate through oxidative esterification. Regardless the two different processes, isobutene (or t-butanol) in solid phase and the corresponding oxidation reaction for manufacturing catalyst of methacrolein are the main technical cores for the industrial production process.
There are lots of patents disclosing the process of isobutene (or t-butanol) to produce MAL and nearly all such patents teach the catalyst containing four major elements which are Mo, Bi, Fe, and Co in the composition. According to these patents, the common objective is that the four major elements incorporating with some trace elements are used to form the catalyst such that the trace elements are adjusted to achieve the relatively high activity and selectivity. However, there are two major drawbacks for such catalyst being applied in the industrial production process.
The first drawback is that when isobutene (or t-butanol) is oxidized to form methacrolein, a relatively huge amount of heat is generated, especially when catalyst is applied. The “overheat” not only causes the reaction in an uncontrolled manner but also drains the most main oxidized element Mo during reaction. In addition, the “overheat” will reduce the service life span of the catalyst. Although the Patents CN 1143946A (U.S. Pat. No. 5,728,894) and CN 1596149A (U.S. Pat. No. 7,012,039) teach the addition of Cerium (Ce) to provide thermal stability and reduction resistance to reduce the used up of Mo during reaction and to prolong the catalyst life, such Cerium cannot solve the “overheat” problem during reaction. At the same time, Cerium will reduce the selectivity of methacrolein in the process. Other Patents, such as CN1048540A and JP publication number 10614, suggest the using of inert material to dilute the oxide catalyst so as to enhance the heat conductivity of the oxide catalyst. However, it is inconvenient to dilute and load the oxide catalyst through the partition diluting method especially when the oxide catalyst is used in a relatively large reactor.
Another drawback is that when isobutene (or t-butanol) is oxidized to form methacrolein, the non-reacted isobutene will reduce the conversion rate not only to increase the consumption of raw material but also to reduce the efficiency of the process in an economical manner. In addition, it will poison the oxide catalyst during the second oxidation step of the first process for manufacturing methyl methacrylate, such that the life and activity of the oxide catalyst are greatly reduced. Therefore, in order to stabilize the reaction in a long term manner, the activity of catalyst should be relatively high in the methacrolein manufacturing process or the reaction should be maintained under a higher temperature. However, such two above mentioned methods will reduce the selectivity of methacrolein. All patents, including U.S. Pat. No. 4,217,309, U.S. Pat. No. 4,250,339, U.S. Pat. No. 4,258,217, U.S. Pat. No. 4,267,385, U.S. Pat. No. 4,306,088, U.S. Pat. No. 4,354,044, U.S. Pat. No. 4,446,328, U.S. Pat. No. 4,511,671, U.S. Pat. No. 5,144,090, U.S. Pat. No. 5,245,083, U.S. Pat. No. 5,583,086, U.S. Pat. No. 5,728,894, did not teach how to maintain the high selectivity of methacrolein while the isobutene is under high conversion rate.